Yeast makes bread rise by releasing bubbles of carbon dioxide into the soft dough.

The longer version

Yeast cells feed on the sugars in flour and break them down for energy. Carbon dioxide and alcohol come out of that process, and the gas collects in tiny pockets throughout the dough. Gluten strands stretched during kneading trap those pockets, so the whole mass swells instead of letting the gas escape.

Heat later expands the trapped gas and sets the structure, leaving the open texture of baked bread. Warmth speeds the process, while cold slows it, and too much salt or sugar can draw water out of the cells and hold them back. The same gas production explains the bubbles in fermented drinks.

Where this entry sits

Everyday physics and chemistry hide small wonders in plain sight, from kitchen reactions to the light in the sky. These short facts explain matter, energy, electricity, magnets, sound, and the simple units we use to measure the world. The full list sits on the Science and Physics page, where every entry is listed in order.